A liquid crystal display (LCD) device controls the transmittance of light (turning display ON/OFF by allowing light to pass or blocking light) by controlling liquid crystal molecules that have birefringent properties. Examples of liquid crystal orientation modes of LCDs include: the TN (twisted nematic) mode, in which liquid crystal molecules having a positive dielectric anisotropy are oriented in a 90° twisted state when seen from a direction normal to the substrate; the vertical alignment (VA) mode, in which liquid crystal molecules having a negative dielectric anisotropy are oriented perpendicular to the substrate surfaces; the IPS (in-plane switching) mode, in which liquid crystal molecules having a positive dielectric anisotropy are oriented horizontal to the substrate surface and a horizontal electric field is applied to the liquid crystal layer; the FFS (fringe field switching) mode, and the like.
Liquid crystal display devices are thin, lightweight, and have low power consumption, and thus are widely used in display devices such as televisions, computers, PDAs, and the like. In recent years, the size of liquid crystal display devices has been rapidly increasing, as seen in liquid crystal display televisions and the like, in particular.
In VA mode, liquid crystal with a negative dielectric anisotropy is used, and display is performed by the liquid crystal molecules that are vertically oriented to the substrate surfaces to be horizontally oriented through a vertical electric field, but if a liquid crystal molecule is seen from a different angle, the perceived birefringence of the liquid crystal molecule changes, and thus causes a problem of having narrow viewing angles.
In order to widen the viewing angles in VA mode, linear projections or electrode slits are provided as orientation regulating structures for multi-domain vertical alignment (MVA) modes. This makes it possible to control the liquid crystal orientation direction when a voltage is applied such that the liquid crystal molecules are oriented in a plurality of directions, even without applying a rubbing treatment to the alignment films, thereby making it possible to obtain viewing angle characteristics that are superior to the conventional TN mode. It is also possible to improve viewing angle characteristic by forming a polymer layer (PSA/polymer sustained alignment) on the substrate and dividing the orientation or the like. A method of dividing orientation has been proposed in which voltage is applied to a liquid crystal layer having light-curable monomers in order to orient the liquid crystal molecules into a plurality of different directions along micro-slits formed in the pixel electrodes. Ultraviolet rays are radiated when the orientation directions are stable in order to harden the light-curable monomers, thereby securing the directions in which the liquid crystal molecules tilt (Patent Documents 1 to 3, for example).
In IPS mode, display is performed by using a horizontal electric field that occurs between a pair of comb-shaped electrodes and by taking advantage of the nature of liquid crystal molecules trying to become horizontally oriented to the electric field. In FFS mode, display is performed by using a horizontal electric field (fringe electric field) that occurs between a common electrode and pixel electrode with an insulating layer therebetween and by taking advantage of the nature of liquid crystal molecules trying to become horizontally oriented to the electric field. The viewing angles are improved in IPS mode and in FFS mode, but it is difficult to obtain a contrast ratio similar to VA mode.
Furthermore, recently, there has been new research in controlling the driving of the liquid crystal in display devices that conventionally perform display by using a horizontal electric field, such as IPS mode or FFS mode devices, by generating an additional vertical electric field (see Patent Documents 4 and 5, for example).